The present invention relates to a depth of interaction detector with uniform pulse-height, which is a scintillation radiation detector having a function of detecting radiation depth of interaction and a function of selecting radiation absorption energy imparted thereto.
Conventionally, there has been known a three-dimensional depth of interaction detector (see, for instance, Document 1 as will be given later) as a depth of interaction detector, which is a scintillation radiation detector having a function of detecting radiation depth of interaction and a function of selecting radiation absorption energy imparted thereto. In this detector, however, the conditions set for absorbed radiation energy may vary depending on every scintillation cell and they must thus be selected independently or individually. For this reason, this detector never has a structure in which radiation energies are selected through a circuit on the basis of the same selection conditions or the same signal-processing circuit. This not only complicates the structure of such a signal-processing circuit for a multi-layer scintillation block obtained by stacking up scintillator cells, but also suffers from a problem in that images thus obtained are non-uniform because the energy resolution capacity of the scintillator cells differ from one another. In other words, there is observed, for scintillator cells located far away from a light-receiving element, a decrease of the sum of output signals due to such stacking up of the scintillator layers and accordingly, the overall depth of interaction-detecting characteristics and energy-resolving characteristics of the device would be damaged.
FIG. 7 shows an example of a conventional depth of interaction detector and FIG. 8 shows the energy spectrum of energy distribution observed for each scintillator cell with respect to the total quantity of light rays received by the light-receiving element of the conventional depth of interaction detector (1) wherein the pulse-heights observed for a γ-ray of a single wavelength considerably differ from cell to cell (see, for instance, Document 2 as will be given later). Thus, the conventional detector would require the use of an amplifier having a wide dynamic range and a digital processing ability upon the processing of signals output from the detector and this makes the design of a front-end processing circuit difficult.
To obtain the same pulse-height for the sum of signals irrespective of which scintillator cell indeed emits light rays, there has been used an optical attenuation technique such as the replacement of a part of the light-reflecting material surrounding cells located in the proximity to the light-receiving element with a light-absorbing material (see, for instance, Document 3 as will be given later). However, this method suffers from a problem such that all of the abilities of resolving energy, position (depth of interaction) and time are deteriorated because of the reduction of the quantity of light capable of being utilized by the light-receiving element.    Document 1: Japanese Un-Examined Patent Publication Hei 1-229995    Document 2: Japanese Un-Examined Patent Publication Hei 11-142523    Document 3: IEEE, Nuclear Science, 1998, Vol. 45(3), pp. 1152–1157